SAN FRANCISCO—A magnitude 6 earthquake jolted both sides of the California-Nevada border, tossed boulders onto a major roadway, and was felt as far off as Las Vegas and even San Francisco, with days of aftershocks predicted, authorities said. The quake shortly before 4 p.m. Thursday was centered south of Lake Tahoe near Walker, a rural community of a few hundred households in the eastern Sierra Nevada. No major damage or injuries were reported, authorities said. It was followed by dozens of aftershocks, including at least a half-dozen of magnitude 4 or above, according to the U.S. Geological Survey. “The ground was shaking pretty bad, and then everything started falling,” said Carolina Estrada, manager at Walker Coffee Company. Syrup bottles broke, dishes fell to the ground and the roof of the shop caved in a bit. The shaking lasted 30 seconds or more, she said. “We ran out of the building,” …